All modern automobiles include a window lift assembly for raising and lowering windows in the door of the vehicle. The most common type of window lift assembly incorporates a "scissor mechanism." As shown in FIG. 1, a scissor-type system includes a door 10, a window 12 vertically moveable within the door 10, a horizontal support bracket 14 on the window 12, and a scissor mechanism 16 supported on the door 10 and engaged with a track 17 on the support bracket 14. A sector rack 18 is supported on the scissor mechanism 16, and a pinion gear 20 supported on the door 10 is engaged with the sector rack 18. In vehicles with power windows, a worm gear 22 driven by a motor 24 is engaged with a driven gear 26 which, in turn, is operatively joined to the pinion gear 20. The motor 24, worm gear 22, and driven gear 26 are all mounted to the door 10 of the vehicle. In vehicles without power windows (not shown), the pinion gear is driven by a manual hand-crank.
Unfortunately, the scissor-type mechanism includes many drawbacks such as the large amount of space and numerous parts required. The scissor-type mechanism is also mechanically inefficient, prohibiting the use of light-weight materials and requiring the use of relatively large motors to drive the system. The large motors necessarily require increased space and electrical power and also increase the weight of the system. With the limited space in a scissor-type system, in order to provide the required torque transfer efficiency it is necessary to have a small diameter pinion gear, typically 0.5 to 0.75 inches, and relatively large driven gear, typically 1.8 to 2.5 inches in diameter, with a gear ratio between the worm gear and driven gear in the 40:1 to 60:1 range. This results in excessive worm gear speed in the range of 3000 to 4000 RPM which causes excessive driven gear tooth shock and armature noise. The combination of high torque, typically 80 to 125 inch-pounds at stall, and shock due to high worm speeds mandates that either expensive multiple gears and/or single driven gears with integral shock absorbers be utilized.
In U.S. Pat. No. 4,167,834 to Pickles, a more mechanically efficient vertical rack and pinion window lift system is disclosed. This type of system is represented in FIGS. 2 and 3 and includes a door 28, a window 30 vertically moveable within the door 28, a support bracket 32 on the window 30, a vertical rack 34 supported on the door 28, and a pinion gear 36 supported on the support bracket 32 in engagement with the rack 34. A motor 38 is supported on the support bracket 32 on the same side of the window 30 as the rack 34 and pinion gear 36 and drives the pinion gear 36 through a worm gear/driven gear transmission (not shown) engaged with the pinion gear 36. The pinion gear 36 is continually meshed with the rack 34 to drive the window 30 up and down. Obvious advantages of this system are the mechanical efficiency, fewer parts and, hence, reduced weight, and reduced motor size. The system is also more simple to install than the scissor-type system.
The Pickles window lift assembly, while theoretically plausible, does not function adequately due to the complex method and arrangement used to adapt the support bracket 32, motor 38, worm gear, and driven gear to the window 30. As discussed in U.S. Pat. No. 4,967,510 to Torii et al., in window lift systems of the type shown in FIGS. 2 and 3 (such as the Pickles system) a larger torque than necessary is required to drive the system due to the angular moment set up by the weight of motor 38 and related structure. In addition, more space than necessary is required due to the "superimposed sequential" stacking of components.
An additional problem with the Pickles system is that a guide member (not shown) is mounted to the support bracket 32 and surrounds the rack 34 to restrict relative movement between the rack 34 and the bracket 32. In addition, the motor 38, associated transmission housing (not shown), and pinion gear 36 are fixedly mounted to the bracket 32 such that the rack 34 and pinion gear 36 are integrally meshed and relative movement is prevented. By preventing any relative movement between the rack 34 and pinion gear 36, the system can bind up or at least provide added resistance to vertical movement, resulting in the need for a larger motor. Binding between a rack and pinion gear is a particular problem given that, as the window is driven upwardly, the window moves in side channels in the door which can place additional torque on the window due to irregularities in the side channels and in the window edges in contact with the side channels. The fact that the window is driven and guided from only a single point on the lower edge of the window further reduces the stability of the window.
The Pickles system also uses a large driven gear and surrounding housing to accommodate an integral, spring based, shock absorbing mechanism (not shown). The large driven gear together with a relatively small pinion mandates that a high motor speed be used, resulting in a noisy operation in order to close the window in a reasonable time frame, such as four seconds.
The system disclosed in the Torii et al. patent improved substantially over Pickles in its functional adaptability. The Torii system is represented in FIG. 4 and includes a window 40, a support bracket 42 on the window 40, a motor 44, a pinion gear 46, and a rack 48. To eliminate the angular moment on the window 40 caused by the weight of the motor 44, the Torii system positioned the motor 44 such that the center of gravity of the motor 44 was substantially aligned with the plane of movement of the window 40. However, as shown in FIG. 4, this arrangement prevents the rack 48 from being positioned as close as possible to the window 40, resulting in an increased angular moment on the window 40 caused by the torque generated at the rack/pinion gear interface acting upon a larger than necessary moment arm L. This angular moment can cause the window to "pull in" in the direction shown by the arrow labeled P.
Although not shown in FIG. 4, the Torii et al. system is similar to the Pickles system by including a guide track integrally joined with the rack and a slide engaged with the guide track and supported on the support bracket. Similar to the Pickles system, this arrangement prevents relative movement between the rack and pinion gear and can cause the system to bind up or provide added resistance to vertical movement. The window is also driven and guided from only a small area on the lower edge of the window which reduces the stability of the window in the same manner as discussed above for the Pickles system.
Therefore, it is desirable to provide a window lift system which includes the benefits of a rack and pinion system while providing smooth operation as the window is raised and lowered and minimizing the torque placed on the window.